1. Field of the Invention
The present invention relates to cam structures. More particularly, the present invention relates to improvements on a cam structure of a compound cam that is equipped with an axial direction cam that displaces one follower section in an axial direction and a radial direction cam that displaces another follower section in a radial direction. The present invention also relates to a disk exchange system that uses the cam structure. The disk may e any disk-shaped recording media including optical disks, such as, CDs (compact discs), DVDs (digital versatile discs) and the like.
2. Description of Related Art
Conventionally, a cam mechanism, in which a rotary cam having step differences in an axial direction is rotated to make a follower section to follow along the step differences and move in the axial direction, has been used. For example, in a cam mechanism shown in FIGS. 67-69, an axial direction cam 101 having three cams 102 that are in the same shape and disposed at intervals of 120 degrees in a circumferential direction is rotated, and a circular plate (follower section) 103 is raised and lowered while moving along the cam 102. In this cam mechanism, the circular plate 103 can be uniformly supported by three regularly disposed protrusions 104 that come in contact with the cams 103.
Also, a cam mechanism, which is equipped with rotary cams with different radiuses arranged in a radial direction and a follower section that is moved in the radial direction along the cams, has been used. For example, a radial direction cam 105 with cams in three stages shown in FIG. 70 is formed from three arcuate surfaces 106 having different radiuses and three connection slopes 107 that connects the three arcuate surfaces 106. A follower section 108 can be moved along the circumferential shape of the cam 105. The arcuate surfaces 106 and the connection slopes 107 shown in the figure are alternately disposed with each of their center angles (i.e., angles of rotation) being 60 degrees.
A rotary member may be equipped with the axial direction cam 101 and the radial direction cam 105 described above. By the rotary member, one follower section (the rotary plate 103) in an axial direction and another follower section (the follower section 108) in a radial direction can be simultaneously displaced. Furthermore, in a compound cam having such a rotary member, movements in various patterns can be realized by one rotary cam by timing the movements of the follower sections 103 and 108. For example, while the follower section 108 may be maintained in one of the stages, and the other follower section 103 may be moved in the axial direction.
However, since the radial direction cam 105 is accompanied with the following limitations, it is sometimes difficult to achieve complex movements by simply combining the axial direction cam 101 and the radial direction cam 105.
Namely, in the radial direction cam 105, the arcuate surfaces 106 that form the respective stages have different radiuses and therefore the three connection slopes 107 that connect these arcuate surfaces 106 necessarily have different inclinations. Therefore, when it is desired that the follower section 108 be smoothly moved in any of the connection slopes 107, the connection slope 107a with a steep inclination that connects the first stage arcuate surface 106 and the third stage arcuate surface 106 preferably have a smaller pressure angle, and needs to secure a wide range (in other words, to make greater the center angle that occupies the connection slope 107a in 360 degrees). By doing so, the ranges occupied by the respective connection slopes 107 become different from one another, which makes it difficult to dispose the arcuate surfaces 120 at equal intervals of 120 degrees. As a result, movements of one follower section in the axial direction are difficult to be timed with movements of another follower section in the radial direction.